A DBS therapy treats an abnormal state of a patient by fixing an electrode to an aimed target (e.g., STN) of a deep brain and continuously applying electric stimulation thereto for a predetermined period.
Since firstly approved in 1998 by U.S. FDA, the DBS therapy has been very popular in the treatment of various brain-controlled disorders including a movement disorder. The DBS therapy has been applied to the treatment of drug induced side effects of patients suffering from essential tremor, rigidity, Parkinson's disease and tremor. In general, this therapy includes positioning a DBS electrode lead through a burr hole drilled into a skull of a patient, and applying proper stimulation signals to a physiological target through the electrode lead. The positioning which includes stereotactic neurosurgical methodology is very important in this therapy, attracts a lot of attention, and becomes a subject of research. Particularly, it is essential to find a deep brain target, continuously position an electrode lead, and efficiently apply stimulation to the target.
To find an optimum physiological target is very difficult in a DBS implantation for treating a movement disorder, particularly, in the treatment of symptoms that cannot be tested on an operating table during an implantation of an electrode lead. For example, in the case of a patient having the Parkinson's disease, postural stability and test walking are substantially impossible during an implantation of a DBS lead. It is also known that rigidity and akinesia, which are two other major symptoms of the Parkinson's disease, are difficult to quantitatively evaluate during an implantation of a DBS lead. In the meantime, intended operation targets include deep brain nuclei or sub-regions in globus pallidus internus or subthalamus. Such structures cannot be easily observed by any of the current imaging modalities, such as magnetic resonance imaging (MRI), computed tomography (CT) and positron emission tomography (PET).
Accordingly, in a conventional DBS implantation, a method wherein a target region is found by means of a kind of template for a brain structure, such as Schaltenbrand-Wahren atlas is used.
In addition, St-Jean et.al. create a 3D structure by stacking a plurality of slices by digitalizing Schaltenbrand-Wahren atlas, and register the 3D structure into a pre-DBS implantation MRI volume data set of a patient by using landmarks, thereby generating a pre-implantation MRI volume data set with the atlas 3D structure put thereon, and finding a target region according to the data set in the DBS implantation.
Recently, a target region is determined on a magnetic resonance (MR) image on the basis of anterior commissural (AC)-posterior commissural (PC) coordinates.
U.S. Pat. No. 7,167,760 gives overall explanations of the DBS therapy, and suggests a method of determining a target region before an implantation which solves the foregoing problems in the prior art.
FIG. 1 is a schematic view illustrating one example of a DBS electrode lead. The DBS electrode lead 100 includes four platinum/iridium contact electrodes 110, 120, 130 and 140. These electrodes 110, 120, 130 and 140 are positioned in a target region, and electric stimulation is applied to some of the electrodes 110, 120, 130 and 140 for treatment.
FIG. 2 is a view illustrating one example of a CT image after an implantation of a DBS electrode, particularly, a post-implantation CT image 400 of a patient after bilateral DBS implantation using two DBS electrode leads 410. Wire leads 420 are connected from the DBS electrode leads 410 to an internal pulse generator (not shown).
Meanwhile, after the DBS electrode lead 400 or DBS electrode is implanted, or after the DBS treatment is finished, whether the DBS electrode has been normally positioned should be evaluated. In the case of using a CT image, according to characteristics of the CT, a DBS electrode is relatively easily found, but a target region which is a soft tissue is not easily found. In the case of using an MRI image, according to characteristics of the MRI, a target region which is a soft tissue is expected to be shown well. However, it is not easy to see the position relation between a DBS electrode and the target region due to an interference of the DBS electrode lead 400 or DBS electrode formed of metal.